During the heating operation of an air conditioner, frost adheres to the outdoor heat exchanger, which reduces the heating capacity. Therefore, it is necessary to remove frost from the outdoor heat exchanger. In order to remove frost, defrosting operation is performed for switching the refrigeration cycle in the air conditioner from the heating cycle to the cooling cycle to cause the outdoor heat exchanger to serve as a condenser. Heat exchange in the heating cycle cannot be performed when the defrosting operation is performed, which reduces the heating capacity. In order not to reduce the heating capacity, it is necessary to avoid unnecessary defrosting operation.
One of the conventionally proposed air conditioners performs defrosting operation if the operation frequency of a compressor in the refrigeration cycle is equal to or greater than the first threshold value and the current flowing in the motor driving the compressor is equal to or less than the second threshold value for more than the third threshold period of time (for example, see Patent Literature 1).